[Lowfer] New Ham band

[lowfer@mailman.qth.net]

At 01:18 PM 01/20/2003 -0600, Tod - Minnesota wrote:
>Regretably, the power company lobbying groups
>have done an about face and declared that such a band could cause 'homeland
>security' problems by hams interfering with PLC's. I suspect the real
>concern is that the power companies do not meet the FCC requirements for
>emmissions from the PLC's.

At UTC's (Utility Telecommunications Council) look into this situation last
fall, rather than seriously look at the facts, they just did the "knee jerk"
response and said, "It won't work."    I had recently left this field of 
endeavor
and unfortunately could not inject any serious input and my former colleagues
mentioned this to me in passing after the session was over, saying, "Gee,
wish you could have been involved..."     Grrr.....   (gritting of teeth!!)

Aside from some minimal radiation (and pickup) using the 3 phase HV
transmission lines, it should be mentioned that PLC receiver sensitivities
are measured more in "volts" than microvolts.  They operate in a high
signal mode to stay above the "line noise" that would be a problem if
trying to receive microvolt type signals that we are used to working with.

Hence, PLC xmtrs usually operate in the area of 10 - 25 watts using a
full length "transmission line" that has a nominal loss of 1dB or less
per mile.   As long as "line tuning" (Z matching 50 ohms from equipment
to the "hundreds of ohms" of the HV line) remains decent,  the
PLC receivers are impervious to any interference.   Interference, if any,
usually shows up when a neighboring power company fires up their
PLC on the same freq.  (and even this is normally coordinated thru UTC)

Consider the minimal signal levels of Amateur/Experimental stations
with extremely low efficiency and they might get signal "pickup"
on a level quite lower than their normal ambient noise......
which, again, is far below their normal operating margin in the high
millivolt range.    Another factor of isolation would be that PLC
"polarity" is necessarily horizontal, and our LF radiation is
necessarily vertical.

Other than that, PLC usage by utilities is at it's lowest point ever,
with all "intelligent" or data type modes being conveyed on Microwave
or Fiberoptic links.   The remaining usage consists mainly of "trip blocking"
signals that are sent to "prevent" unnecessary tripping of substation breakers
when a fault occurs somewhere on a HV path.   If a million to one situation
occurred where a lowfer signal hit exactly on a PLC trip blocking receiver
and was of sufficient strength, it would not cause any harm, but actually
work "in cooperation" with the main purpose of the system..... which is
to PREVENT tripping!   (a PLC rcvr with NO signal present under a fault
condition would allow tripping of the substation breakers)    If a real fault
occurred near a particular substation, there would be no signal conveyed
to the PLC rx in any manner, due to the fault (or shorting condition) on the
HV line killing any signal pickup.

Just so I don't leave anything out, there is another mode called "transfer
trip" which is used to trip breakers at a distance via PLC.   However, this
system uses two to four signals that shift apart in frequency to ensure
a "foolproof" system (not one single freq signal).   Also, at the point of
transmission of a trip signal, this system increases xmit power 10 dB.
No problems here either.......

Sorry for the verbiage, but what this situation needs is some intelligent FCC
input during any comment period....if it is still open.

Perry      w8au